The United Nations began delivering ballots and voting kits across Afghanistan today as hurried preparations for the 7 November runoff in the presidential election got under way.

International election monitors called on the authorities to avert the widespread fraud that marred the first round of voting in August. Scores of election staff accused of misconduct have been sacked and new personnel need to be hired.

President Hamid Karzai will face a former foreign minister, Abdullah Abdullah, in the runoff. Abdullah said yesterday that he was ready to take part, one day after Karzai bowed to intense US pressure and acknowledged he had fallen short of the 50% threshold needed for victory in the original election, held on 20 August. UN-backed auditors threw out nearly a third of Karzai's votes because of fraud.

In Washington, US officials said a power-sharing arrangement between Karzai and Abdullah to avoid a runoff was still possible, although it would be up to the Afghans.

Organising the ballot in a little more than two weeks poses a huge challenge. The preparations come amid a growing Taliban insurgency and before Afghanistan's harsh winter snows, which begin in much of the country around the middle of November.

UN spokesman Dan McNorton said today that UN planes were flying the voting kits to provincial capitals, from where they will be delivered to thousands of polling stations by truck, helicopter and donkey.

The Afghan Independent Election Commission, or IEC, the body that runs the elections, is dominated by Karzai supporters. It is under huge pressure to avoid a repeat of the massive fraud that discredited the government and threatened to undermine public support from the US and European countries that provide most of the 100,000 Nato-led troops serving in Afghanistan.

The International Republican Institute, based in Washington, said that insecurity, ballot box stuffing and the misuse of state resources for campaigning must be addressed for the poll to be credible. The US desperately wants a government that is legitimate in the eyes of Afghans and the international community.

Another US-based monitor, the National Democratic Institute, said more Afghan police and troops would be needed this time. The group said that to eliminate so-called "ghost" polling stations, no ballots should be sent to polling centres that are not secured by Afghan security forces and adequately staffed by the IEC.

It also said that "polling centres that experienced fraud during the original election should receive targeted IEC scrutiny on election day and during the counting process".

In an effort to reduce cheating, officials will cut about 7,000 of the 24,000 polling stations. Some were in areas too dangerous to protect. Others never opened, enabling corrupt officials to stuff the ballot boxes with impunity. About 200 of the 2,950 district election co-ordinators will be replaced after complaints of misconduct.

Finding replacements for co-ordinators and poll workers implicated in fraud will be difficult, especially in a country where more than 70% of the population is illiterate. The government had to scramble this summer to recruit enough election officials and poll workers, especially at voting stations reserved for women.

It is unclear if it will be able to fill open posts with better-qualified people.

Karzai is widely seen as the frontrunner in the race. But Abdullah could pose a challenge if he is able to quickly build a wider coalition.

Former planning minister Ramazan Bashardost, who came in third in the first round, said he had not made up his mind who he would support – if anyone. He said he would meet his supporters next week to decide, but the choice was between "the worst, and worse than the worst."